1. Field of the Invention
This invention relates to heat developable imaging materials and processes for developing an image employing in reactive association (a) photosensitive silver halide, (b) an image-forming combination comprising (i) a silver salt of a certain 1,2,4-mercaptotriazole derivative with (ii) a silver halide developing agent, and (c) a polymeric binder. In one of its aspects it relates to a photothermographic element comprising a support having thereon the described photosensitive silver halide and combination of imaging materials. In another aspect it relates to a photothermographic composition comprising the described photosensitive silver halide and imaging combination. A further aspect of the invention relates to a process of developing an image in a photothermographic material containing the described imaging combination. A further aspect relates to new silver salts of certain 1,2,4-mercaptotriazole derivatives, especially those which are useful in the described imaging combination.
2. Description of the State of the Art
It is known to provide an image in an imaging material, especially a photographic imaging material, by what is known as dry processing with heat. These materials are often described as heat developable photographic materials or photothermographic materials. Such heat developable photographic materials after imagewise exposure are heated to moderately elevated temperatures to provide a developed image in the absence of separate processing solutions or baths. Typical heat developable imaging materials or photothermographic materials are described, for example, in U.S. Pat. No. 3,152,904 of Sorensen et al, issued Oct. 13, 1964; U.S. Pat. No. 3,457,075 of Morgan et al, issued July 22, 1969; U.S. Pat. No. 3,392,020 of Yutzy and Yackel, issued July 9, 1968; and British Specification No. 1,161,777 published Aug. 20, 1969.
The most commonly used silver salts in such heat developable photographic materials are silver salts of long-chain fatty acids, such as silver behenate which generally require hydrophobic binders. It has been desirable to replace these silver salts of long-chain fatty acids to enable use of aqueous or hydrophilic compositions which further enable the use of conventional silver halide emulsion technology in heat developable photographic materials. Use of silver behenate as a source of silver in such heat developable materials is not particularly compatible with aqueous formulations of photosensitive silver halide materials. Other silver salts or complexes have been proposed for such heat developable photographic materials. These include, for example, silver salts of benzotriazole, silver salts of saccharin and related silver salts or complexes. These are described, for example, in heat developable photographic materials in U.S. Pat. No. 3,617,289 of Ohkubo et al, issued Oct. 2, 1971; U.S. Pat. No. 3,666,477 of Goffe, issued May 30, 1972; U.S. Pat. No. 3,672,904 of deMauriac, issued June 27, 1972; U.S. Pat. No. 3,832,186 of Masuda et al, issued Aug. 27, 1974; British Specification No. 1,205,500 published Sept. 16, 1970; U.S. Pat. No. 3,689,270 of Anderson et al, issued Sept. 5, 1972; and German Offenlegungsschrift No. 2,326,865 published Dec. 6, 1973. Other silver complexes or salts in heat developable materials, which include silver salts of nitrogen acids, are described in copending U.S. application Ser. No. 684,699 of deMauriac, filed May 10, 1976. While many of these silver complexes or salts can provide an image in such heat developable photographic materials, they often provide poor processing temperature latitude, poor photographic speed, poor image tone, or a combination of one or more of these problems. The photothermographic materials also in many cases have required the presence of what has been described as "melt-forming compound" to provide a desired developed image.
It is desirable in many cases to spectrally sensitize heat developable photographic materials to enable exposure to other than the blue region of the visible spectrum. Difficulty is often encountered in spectrally sensitizing photosensitive silver halide to be used in heat developable materials. While in many cases some degree of spectral sensitization can be provided, it is often insufficient for many photographic purposes. It has been desirable to provide a heat developable silver halide photographic material based on aqueous photographic silver halide technology which permits use of a broader range of spectral sensitizing dyes.
It has also been desirable to provide heat developable photographic materials containing silver salts of certain heterocyclic compounds that enable use of more conventional silver halide developing (reducing) agents in photographic materials. Heat developable photographic materials often have used unconventional reducing agents which require costly processes of preparation. It has been desirable, for instance, to provide heat developable materials which enable use of more conventional hydroquinone silver halide developing agents, 3-pyrazolidone silver halide developing agents and ascorbic acid developing agents. Typical reducing agents which have been used in photothermographic materials are described, for example, in U.S. Pat. No. 3,672,904 of deMauriac, issued June 27, 1972. Commercially available photothermographic materials have contained, for example, 2,2'-methylene bis(4-methyl-6-tertiary butyl phenol) as a reducing agent, but not conventional silver halide developing agents.
Heavy metal salts of certain heterocyclic compounds, such as heterocyclic azoles, are known in thermographic materials, that is materials in which the visible image is formed by imagewise heating, not by a photographic process. Such heavy metal salts of azoles are described, for example, in thermographic materials in U.S. Pat. 3,767,414 of Huffman et al, issued Oct. 23, 1973. The described thermographic materials, however, are not photographic materials.
Silver salts of a variety of heterocyclic compounds are known for various purposes in photographic materials. Such uses of silver salts are described, for example, in U.S. Pat. No. 2,353,754 of Peterson, issued July 18, 1944 and U.S. Pat. No. 3,794,496 of Manhart, issued Feb. 26, 1974.
A common problem encountered in heat developable photographic materials centers on instability of the image following processing. This is usually manifested by print-up following processing. Often heat developable photographic materials have required addition of a separate post-processing image stabilizer or stabilizer precursor to provide desired post-processing stability. Examples of stabilizer precursors in photothermographic materials are described, for instance, in U.S. Pat. No. 3,839,041 of Hiller, issued Oct. 1, 1974. This added component, however, increases the cost of the heat developable material.
There has been a continuing need for improved photothermographic materials which have the improved photosensitivity provided by a photosensitive silver halide material and which enable use of conventional gelatino silver halide emulsion technology. There has also been a continuing need for improved photothermographic materials which enable improved post-processing image stability in the absence of a separate image stabilizer or stabilizer precursor. It has also been desirable to provide a heat developable photographic material as described in which silver development efficiency is improved, such as above about 50%. There has been a further need to provide new silver salts of certain 1,2,4-mercaptotriazole compounds that enable the described advantages in photothermographic materials and processes.